In an ink-jet recording head, a voltage applied to a piezoelectric device formed on a vibration plate causes a momentary change in the volume of a pressure chamber that communicates with nozzles and increases the pressure therein. The increased pressure causes ink droplets to be ejected from the nozzles and onto a recording medium.
For a conventional ink-jet printer, a piezoelectric ceramic layer made of lead zirconate titanate (PZT), for example, is formed on one face of a pressure chamber substrate to provide a piezoelectric device. Preferably, a polarized piezoelectric device is employed.
A desired improvement for the piezoelectric device used in an ink-jet printer is the capability to provide a greater displacement upon application of a smaller drive voltage. Physically, this characteristic can be quantified by using a value obtained from piezoelectric constant d, which is a product of piezoelectric constant g and a dielectric constant. The piezoelectric constant d is a factor of proportionality derived from a displacement and an electric field, and the piezoelectric constant g is a factor of proportionality between an electric field and stress. The dielectric constant is a factor of proportionality between the applied electric field and the density of a charge on a surface.
However, when an experiment is conducted while changing the composition of a piezoelectric ceramic material used to form a piezoelectric device in order to obtain the desired characteristic for an ink-jet recording head, it is difficult to obtain a single piezoelectric ceramic composition having a satisfactory piezoelectric constant d.
Accordingly, it is a first object of the present invention to provide an ink-jet recording head that has a laminated structure comprising piezoelectric ceramic layers having different characteristics, so that a piezoelectric device can be formed which has a higher piezoelectric constant d than a conventional device, thereby permitting more ink droplets to be ejected at a higher speed while applying a lower voltage.
It is a second objective of the present invention to provide a method, for manufacturing an ink-jet recording head, that comprises a step of laminating a plurality of piezoelectric ceramic layers having different characteristics, so that a piezoelectric device can be formed which has a higher piezoelectric constant d than a conventional device, thereby permitting more ink droplets to be ejected at a higher speed while applying a lower voltage.
It is a third objective of the present invention to provide a piezoelectric device that has a laminated structure comprising piezoelectric ceramic layers having different characteristics, and that, therefore, has a higher piezoelectric constant d than a conventional device.